Diosbulbin B

Ferulic acid prevents liver injury and increases the anti-tumor effect of diosbulbin B in vivo.[Pubmed: 24903991]

J Zhejiang Univ Sci B. 2014 Jun;15(6):540-7.

METHODS AND RESULTS:
The present study is designed to investigate the protection by ferulic acid against the hepatotoxicity induced by Diosbulbin B and its possible mechanism, and further observe whether ferulic acid augments Diosbulbin B-induced anti-tumor activity. The results show that ferulic acid decreases Diosbulbin B-increased serum alanine transaminase/aspartate transaminase (ALT/AST) levels. Ferulic acid also decreases lipid peroxide (LPO) levels which are elevated in Diosbulbin B-treated mice. Histological evaluation of the liver demonstrates hydropic degeneration in Diosbulbin B-treated mice, while ferulic acid reverses this injury. Moreover, the activities of copper- and zinc-containing superoxide dismutase (CuZn-SOD) and catalase (CAT) are decreased in the livers of Diosbulbin B-treated mice, while ferulic acid reverses these decreases. Further results demonstrate that the mRNA expressions of CuZn-SOD and CAT in Diosbulbin B-treated mouse liver are significantly decreased, while ferulic acid prevents this decrease. In addition, ferulic acid also augments Diosbulbin B-induced tumor growth inhibition compared with Diosbulbin B alone.
CONCLUSIONS:
Taken together, the present study shows that ferulic acid prevents Diosbulbin B-induced liver injury via ameliorating Diosbulbin B-induced liver oxidative stress injury and augments Diosbulbin B-induced anti-tumor activity.

Diosbulbin B-induced liver injury in mice and its mechanism.[Pubmed: 24107456]

Hum Exp Toxicol. 2014 Jul;33(7):729-36.

Dioscorea bulbifera L., a commonly used medicinal plant in China, is reported to induce hepatotoxicity. The present study is undertaken to investigate the hepatotoxicity induced by Diosbulbin B (DB), a diterpene lactone isolated from D. bulbifera L., and to further explore its underlying mechanism.
METHODS AND RESULTS:
DB was administered to mice at the doses of 0, 16, 32, and 64 mg/kg once daily for 12 consecutive days. Liver injury induced by Diosbulbin B was evidenced by the increased activity of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP). Liver histological evaluation showed that the mice treated with Diosbulbin B exhibited liver damage with the swelling of hepatocytes. Further results showed that the amount of malondialdehyde (MDA) in the liver was increased in mice treated with Diosbulbin B, while the glutathione amount and the enzymatic activity of glutathione peroxidase (GPx), glutathione-S-transferase (GST), copper/zinc-superoxide dismutase (CuZn-SOD), manganese-SOD (Mn-SOD), and catalase (CAT) were all decreased. Diosbulbin B also decreased the gene expression of CuZn-SOD and CAT.
CONCLUSIONS:
Taken together, our results indicate that oral administration of Diosbulbin B for 12 consecutive days can lead to the oxidative stress liver injury in mice.

Cytochrome p450-mediated metabolic activation of diosbulbin B.[Pubmed: 25024403]

Metabolism of diosbulbin B in vitro and in vivo in rats: formation of reactive metabolites and human enzymes involved.[Pubmed: 25053620]

Drug Metab Dispos. 2014 Oct;42(10):1737-50.

Diosbulbin B (DB), a major constituent of the furano-norditerpenes in Dioscorea bulbifera Linn, exhibits potential antineoplasmic activity and hepatotoxicity. The metabolism and reactive metabolites of Diosbulbin B in vitro (with human and animal liver microsomes) and in vivo in rats were investigated.
METHODS AND RESULTS:
The human enzymes involved in DB metabolism were identified. Diosbulbin B was first catalyzed into reactive metabolites of 2-butene-1,4-dial derivatives dependent on NADPH and then trapped by Tris base or oxidized to hemiacetal lactones (M12 and M13) in microsomal incubations. Tris base was used as buffer constituent and as a trapping agent for aldehyde. Methoxylamine and glutathione (GSH) were also used as trapping agents. Diosbulbin B metabolism in vivo in rats after oral administration was consistent with that in vitro. The structures of M12 and M13, as well as mono-GSH conjugates of Diosbulbin B (M31), were confirmed by nuclear magnetic resonance spectroscopy of the chemically synthesized products. The bioactivation enzymes of Diosbulbin B were identified as CYP3A4/5, 2C9, and 2C19. CYP3A4 was found to be the primary enzyme using human recombinant cytochrome P450 enzymes, specific inhibitory studies, and a relative activity factor approach for pooled human liver microsomes. Michaelis-Menten constants K(m) and V(max) were determined by the formation of M31.
CONCLUSIONS:
The reactive metabolites may be related to the hepatotoxicity of Diosbulbin B. The gender difference in CYP3A expression in mice and rats contributed to the gender-related liver injury and pharmacokinetics in mice and rats, respectively.

Drug Metab Dispos. 2014 Oct;42(10):1727-36.

Diosbulbin B (DIOB), a furan-containing diterpenoid lactone, is the most abundant component of Dioscorea bulbifera L. (DB), a traditional Chinese medicine herb. Administration of purified Diosbulbin B or DB extracts has been reported to cause liver injury in animals. The mechanisms of Diosbulbin B-induced hepatotoxicity remain unknown. The major objective of this study was to identify reactive metabolites of Diosbulbin B.
METHODS AND RESULTS:
A Diosbulbin B-derived cis-enedial was trapped by N-acetyl lysine (NAL) and glutathione (GSH) or N-acetyl cysteine (NAC) in rat and human liver microsomal incubation systems after exposure to Diosbulbin B. Four metabolites (M1-M4) associated with GSH were detected by liquid chromatography coupled to tandem mass spectrometry. Apparently, M1 was derived from both NAL and GSH. M2 and M3 resulted from the reaction of GSH without the involvement of NAL. Two molecules of GSH participated in the formation of M4. M2 and M3 were also detected in bile and urine of rats given Diosbulbin B. M5, a Diosbulbin B-derived NAC/NAL conjugate, was detected in microsomal incubations with Diosbulbin B fortified with NAC and NAL as trapping agents. Biomimetic M1-M5 were prepared by oxidation of Diosbulbin B with Oxone for metabolite identification.
CONCLUSIONS:
Microsomal incubation study demonstrated that ketoconazole inhibited the production of the enedial in a concentration-dependent manner, and CYP3A4 was found to be the enzyme responsible for the metabolic activation of Diosbulbin B. The metabolism study facilitates the understanding of the role of bioactivation of Diosbulbin B in its hepatotoxicity.